Carb/Weather Question...?
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Carb/Weather Question...?

  1. #1
    Super Moderator HammerDown's Avatar
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    Default Carb/Weather Question...?

    Question...if a carb has not been readjusted/touched from humid hot summer months and the cool,dry season sets in >would the spark plugs show rich or lean?
    I would think lean, as cool air is more dense and being ingested into the mix...no?
    <img src=http://www.performanceboats.com/gallery/data/500/medium/06-30-11_1234.jpg border=0 alt= />

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  3. #2
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    Default Tip of the iceburg

    Quote Originally Posted by HammerDown View Post
    Question...if a carb has not been readjusted/touched from humid hot summer months and the cool,dry season sets in >would the spark plugs show rich or lean?
    I would think lean, as cool air is more dense and being ingested into the mix...no?
    There are volumes written about fuel/air ratios and weather. Hot to cold doesn't necessarily mean better air. If you have a baseline tune up in one weather condition, and some sort of meter to read air density/corrected altitude, you can dial the engine air/fuel right back to where it was....BUT, (big but), if you have 10% less air to mix 10% less fuel with, the end resulting power WILL be 10% less......IMO, if you feel you have better air now than in the hot summer months, step the jets up 2 sizes and test the boat. If you see a remarkable improvement from a CURRENT baseline, try 2 more jet sizes. Before you do anything, test the boat and record the results using good instruments, (timing light,tach,GPS) and establish a baseline to work from. Write everything down and only compare apples to apples. AND!!! ONLY CHANGE ONE THING AT A TIME.............Unless you're running the engine right on the edge, the difference may not even be noticeable......Of course if your summer tune up was way off, you might see a big difference un related to weather...........Ray
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    Super Moderator HammerDown's Avatar
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    Default

    Thanks for the detailed feedback Ray.
    I should have mentioned my question was about my Harley-Shovel with it's dual throat Dellorto sidedraft carb.
    During the hot humid days of summer plugs are nice and clean. As the cool, dry weather hits they show to be fat/rich. Where I figured they would go leaner.
    Engine is still very drivable and makes strong power...just noticing the plugs being a bit darker at 65 degrees/fall temps vs 95 hot-muggy degrees/mid summer.
    <img src=http://www.performanceboats.com/gallery/data/500/medium/06-30-11_1234.jpg border=0 alt= />

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    blown mopar moparjet's Avatar
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    Default

    hey ray..
    might be due to the engine temp itself..gonna run colder on a cool day compaired to a hot day when the engine is at a hotter temp. that motor is air cooled right?.. i run an old air/oil cooled suzuki prostreet dragbike.. it does like the cool weather but engine needs to be as hot as it can get before a pass..
    throw it in reverse

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    Default Oh, cool...

    Quote Originally Posted by HammerDown View Post
    Thanks for the detailed feedback Ray.
    I should have mentioned my question was about my Harley-Shovel with it's dual throat Dellorto sidedraft carb.
    During the hot humid days of summer plugs are nice and clean. As the cool, dry weather hits they show to be fat/rich. Where I figured they would go leaner.
    Engine is still very drivable and makes strong power...just noticing the plugs being a bit darker at 65 degrees/fall temps vs 95 hot-muggy degrees/mid summer.
    Same air fuel ratios apply to any internal combusted engine......I'm betting your driving habits have changed a bit from the lazy hazy days of summer..............Seriously, a tune up is a tune up.............Ray
    LOUD BOATS SAVE LIVES

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